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Date: Sun, 04 Jul 2021 09:38:25 -0500
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Subject: Re: [PHP-DEV] [RFC] Pipe Operator, take 2
From: larry@garfieldtech.com ("Larry Garfield")

On Sun, Jul 4, 2021, at 2:18 AM, Olle H=C3=A4rstedt wrote:
> 2021-07-04 4:12 GMT+02:00, Larry Garfield <larry@garfieldtech.com>:
> > On Mon, Jun 7, 2021, at 2:00 PM, Larry Garfield wrote:
> >> Hi folks. Me again.
> >>
> >> A year ago, I posted an RFC for a pipe operator, |>, aka function
> >> concatenation.  At the time, the main thrust of the feedback was "c=
ool,
> >> like, but we need partial function application first so that the sy=
ntax
> >> for callables isn't so crappy."
> >>
> >> The PFA RFC is winding down now and is looking quite good, so it's =
time
> >> to revisit pipes.
> >>
> >> https://wiki.php.net/rfc/pipe-operator-v2
> >>
> >> Nothing radical has changed in the proposal since last year.  I hav=
e
> >> updated it against the latest master.  I also updated the RFC to us=
e
> >> more examples that assume PFA, as the result is legit much nicer.  =
i
> >> also tested it locally with a combined partials-and-pipes branch to=

> >> make sure they play nicely together, and they do.  (Yay!)  Assuming=
 PFA
> >> passes I will include those tests in the pipes branch before this o=
ne
> >> goes to a vote.
> >
> > Hi again.
> >
> > With PFA being declined, I've again reworked the Pipes RFC.
> >
> > 1) It now does not use PFA in any examples, but it does use Nikita's=

> > first-class-callables RFC that looks like it's going to pass easily.=

> >
> > 2) With major hand-holding from Levi Morrison and Joe Watkins, the
> > implementation has shifted a bit.  It now evaluates left-to-right, a=
lways,
> > whereas the previous version evaluated right-to-left.  That is, inst=
ead of
> > $a |> $b |> $c desugaring into $c($b($a)), it now becomes effectivel=
y $tmp =3D
> > $a; $tmp =3D $b($tmp); $tmp =3D $c($tmp);  That matters if $b or $c =
are function
> > calls that return a callable, as they are then only called when the =
pipeline
> > gets to that part of the expression.
>=20
> Hi! Can you flesh out an example for this, please? Not sure I get the
> use-case where it matters. Couldn't find any example inside the PR
> either (the tests) that show-cased this particular implementation
> detail. Did I miss it?

The "evaluation order" test is for exactly that:

https://github.com/php/php-src/pull/7214/files#diff-526802c5ee7e0aa37afd=
67683d2c8b73c923b445737b3b44fae6bb5ea117ee97

With the old desugaring way, _test2() was called first before anything e=
lse.  With the new way, it's called after _test1(), as most people would=
 expect from reading it.

--Larry Garfield